Frequency checking TGSL question

[waltr]

Yes, Nulling adjustment is very sensitive. Nice setup to hold coils and adjust.

The 60 second and then beeping sounds like it might be in later stages.

Check outputs of U104 & U105 without a target. Scope should show no AC and DVM in the mV range.
Then back to outputs of U103a & b should also be near 0V.

Is your GB pot a trimmer on the PCB or panel mounted. I did the PCB trimmer and this adjustment is also very sensitive.
If a panel pot then yes, connect pot case to ground lead.


Last for now, The coil picks up all kinds of EM from electrical and electronic stuff in the house.
This can made it very hard to impossible to make adjustments.

[billr]

It's alive. It lives
Ok so. New BF245's arrived I replaced TR5 with the known bad one and that changed a lot of anomalies. So I went one stage further and changed out TR4.......Just because I ordered two. Dang what a difference that made. Everything from step 5 suddenly made sense in the manual.

Until the change out I really though the author was drunk at the time of writing cuz I got diddly on my scope that looked anything like the screenshots.
What I learned from this is to NEVER buy components from a none reputable source. When I checked the 'good' one I'd removed it was way off base to the new ones value. Lesson learned.

I still need to adjust the two caps for RX and TX as I'm running approx 12uS between them and the coils I made could be better.
If anyone has a starting point value they can suggest to adjust the caps in parallel I would appreciate it. Did think about adjustable caps but they only go up to 200pF and I may need to go more than that. This procedure is new to me.

For now, with a few tweaks to go I am getting:
12.5" (32cm) with a British copper 2 pence coin. Approx dollar coin size but not weight.
12" (30.5cm) with a 1 euro coin
Both air tests and measured at the point the sharp clear tone fades to much less.

This has been a good project for me to learn from. I've really tried to think it through before posting for help. That helped me pick up a lot more than I world normally have done. May have posted a few erroneous pics in my last post due to the bad readings I was getting and unfamiliarity with the new scope.

I want to thank you waltr and Andy from diydetector.co.uk
You both helped more than you know. And Andy if your reading this. Sorry for the dumb question/rant about the board not having two LF353's but the schematic did. I often have brain cell meltdowns.

Have a great Christmas guys if I don't catch you before then.

[kt315]

br, believe me now chinese tester is perfecto. use it in every your check everytime.
look my album https://www.geotech1.com/forums/albu...chmentid=45436

[billr]

Hi kt
Thank you for that. I will look into buying one.
A self appointed Christmas present sounds perfect to me.
I'm using the slow method of testing transistors with the multi meter on diode setting which is OK but takes longer to figure out which pins are GDS. It seems there are 3 varieties of the BF245c. I know D & S are interchangeable but some versions have G in the center pin.

[kt315]

i have them two. first i bought like a kit. its working perfecto. second i bought in ready form.
i like those contact pins' sockets on the housing. right done by the master hand.
in first i added two sockets on housing for probes with wires. that stands up a comfort using.
also, you have to remember to discharge big-value-big-voltage caps before the testing, anotherway you can burn the tester.

[billr]

That's good to know kt. Yes discharging does bring with it a few surprises sometimes. I retro fitted a welder of mine with a rectifier and large cap but forgot to discharge it when testing. My workshop looked like the 4th of July for a second or two . Have bookmarked a link to your tester but will order after Christmas as I'm sure it will become lost in the mail this time of the year.

Speaking of caps. This to anyone who wants to throw it out there.
I noticed when I fire up the TGSL it takes about 10 seconds before the detector audio becomes apparent through the speaker. The signal is instant on the scope but not sound........almost like the caps need charging.
If I switch off and count to 10 then restart the audio is instantaneous as if the caps have not discharged.
Not a problem to me but have to ask is this normal? If not can someone advise on a checklist / fix?
Behaves almost like an old tube CB radio.

[billr]

One of the posts above prompted me to describe my method of achieving absolute null to a given coil configuration. So thought I would add my very limited understanding of electronics to this thread with regards to it. For those who want to build the TGSL in future and encounter problems during the nulling phase. Here is what I did.

1. Follow the manual suggestions either using the basic or advanced method described within. I found this got me close but not to the limit of what could be achieved.
2. Make a coil setup with nylon screw as I did in post #15. Setup pic.
3. Get yourself a plastic ruler and copper coin. Silver coin may contain too much iron depending on what it is, where from etc. I found cu best for testing.

Once null is achieved in accordance with the manual procedure.

4. Range check the coils by holding the ruler vertical in the center of the coil whilst passing the coin over and upward, as if trying to see how far you can detect until the detection beep fades. (this is the maximum detection range on the coil you are testing according to your test equipment)
5. Identify the range on the ruler and take note. This now becomes the baseline.
6. Adjust the nylon screw in or out a 1/4 turn and re test.
7. At some point you will max out the detection range of the coin and it will start to decline down the ruler. If turned the wrong way from the start of the test, the range will decrease from what you had at the beginning. Time to go the other way and re check.
8. Adjust the screw a 1/4 turn at a time until it tops out. You have now reached the max limit potential of the coils in their configuration. Regardless of what the meter or scope says.

Looks like a lengthy process when written down but actually works out as being nothing more that a how far can I stretch this range exercise.
I added 3/4" (20mm) on to my detection range compared to what my scope and meter said was the max.
Others may be able to add more.

Good hunting.

[waltr]

Great news. Yes, I always buy parts from good sellers. Generally I buy from DigiKey or Mouser (I think Mouser now has a EU presence).

An do check transistor (FETs) for correct pin-out. This has gotten me a few times.

Sounds like you do NOT need to play with the TX, RX caps. But if you wish to remember that caps in parallel Add, so to increase C (decrease Frequency) hold, or solder, another cap onto the existing cap. I used 1nf to 10nF caps for this.
Then redo your Nulling procedure looking for 'greatest distance'.


I kind of did that same finial Null procedure without thinking.
Good write up on doing that and having an adjustment screw is very helpful.

Now get out there and find some ancient treasure...

[Tibuck19]

With the issues im having with the IDX, i want to venture in getting a bigger and better coil for the TGSL,I am having a hard time locating the info im sure i read somewhere in here that i need a 5 pin tesoro coil ? however if i look at the widescans the 5 pins are made for the umax... which operate at 10khz and the 4 pin coils are used for the Vaqueros... which run at 14.5khz, Would the 4 pin not be better suited for the TGSL?

[SWL]

Hello! I haven't done TGSL for a long time and forgot. How to properly connect TX to frequency counter to tune to the frequency? Thank you!

[waltr]

Hello! I haven't done TGSL for a long time and forgot. How to properly connect TX to frequency counter to tune to the frequency? Thank you!

I use a scope and connect as in #2, across the coil.
If the probe, freq counter or scope input, is high enough impedance it will not load the TX oscillator or add any significant C.

[SWL]

Thank you so much!